Conventionally, a variety of gasification facilities have been proposed. For example, there is a so-called two-tower circulating fluidized bed gasification facility comprising gasification and combustion furnaces (see Patent Literature 1).
In the gasification furnace constituting the two-tower gasification facility, steam is fed from below to provide a fluidized bed of bed material (such as silica sand or limestone) for gasification of a raw material (such as coal, biomass or tire chips) charged from above to thereby produce a produced gas and unreacted char. The produced gas produced in the gasification furnace is taken out through a lead-out passage to outside, and a mixture of the unreacted char produced in the gasification furnace with the bed material is introduced into the combustion furnace through a lead-in pipe.
In the combustion furnace constituting the two-tower gasification facility, blow-up air is fed from below to provide a fluidized bed for combustion of the unreacted char from the gasification furnace to thereby heat the bed material. Blown-up combustion exhaust gas is introduced into a material separator such as a hot-cyclone where it is separated into the bed material and exhaust gas; the separated bed material is supplied to the gasification furnace.
The above-mentioned two-tower gasification facility has a feature that gasification of raw material can be prolonged by increasing a capacity of the gasification furnace to thereby effectively gasify the raw material even if the raw material is for example coal containing much fixed carbon.
Upon start-up of the two-tower gasification facility, especially, upon cold startup, firstly the bed material must be heated to a temperature which enables the gasification of raw material; conventionally, fuel such as LNG, LPG or light oil is burned for such heating. It is, however, problematic that a considerable cost is required for the heating of the bed material since a large amount of fuel such as LNG, LPG or light oil is needed for heating a large amount of bed material housed in gasification and combustion furnaces with large capacities as in the two-tower gasification facility up to a temperature which enables the gasification of raw material and such fuel is relatively expensive. Moreover, upon start-up and shutdown of the gasification facility which produces a flammable produced gas, the gasification furnace and the lead-out passage for the produced gas must be purged with inert gas to ensure safety; conventionally, inert gas such as nitrogen (N2) is fed for such purge. It is, however, problematic that cost for the purge increases since the purge of the gasification furnace generally requires an amount of inert gas about five times greater than the capacity of the gasification furnace and therefore a large nitrogen producer is required.
Thus, for a gasification facility, a technique has been desired to be developed which can reduce the cost required for heating the bed material especially upon cold startup of the gasification facility and which can effectively and inexpensively perform an operation of purging a gasification furnace and a lead-out passage for produced gas; however, currently such a technique has not been proposed.                [Patent Literature 1] JP 2005-041959A        